Disc brakes for railway cars generally include an outer braking ring having two spaced-apart braking surfaces that are connected together by a plurality of cooling vanes or webs. These outer braking ring members are generally made from some material which provides a good braking surface, such as cast iron. The outer braking member is connected to and supported by an inner member or hub. The hub is usually made of a different material, such as cast steel. Accordingly, any means used for connecting the inner or hub member to the outer braking ring must not only secure and support the two, but must also accommodate the expansion and contraction of the braking ring.
Early attempts to fashion disc brake assemblies generally called for an inner, bell-shaped hub having fingers radially extending in one direction from the hub toward the braking disc. Then the braking disc was coupled to the extending fingers by a bolt, or interference fit, or braising, or any one of the foregoing. See, for example, U.S. Pat. Nos. 2,412,432; 2,621,762; and 2,603,316. As the railway vehicles became larger, thereby generating higher thermal and inertial loads, the foregoing assemblies cracked under the large stresses placed on the assembly members, particularly at their connecting points.
Current disc brake assemblies are subjected to high torque and thermal load during normal braking. Torque produced by the friction of the brake pads is transmitted from the disc assembly to the wheels. A large thermal load, also due to the friction, thermally expands the disc in axial and radial directions. With these loads on the disc, a connecting member which supports the disc to the hub assembly must be able to allow for the thermal expansion of the disc while transmitting the braking torque to the hub.
In U.S. Pat. No. 4,083,435, one method for accommodating this expansion and contraction is to provide a highly precisely machined interference fit between the disc and the hub. In that patent, an extension of a vane of the outer braking ring fits snugly into a groove of the inner hub. Other methods for mounting an outer disc to an inner hub are shown in U.S. Pat. Nos. 4,108,826 and 4,077,501. The former provides a plurality of clamping sleeves seated in radially opposed bores in the hub and the outer ring. The latter provides a plurality of lugs that are integral with the cooling vanes and extend radially from the braking ring toward the hub. Specially formed slots in the lugs accommodate a bolt that fixes the lug portion to a portion of the hub. The specially formed slots are fashioned to provide for the necessary expansions between the hub and the braking ring.
Another current disc brake assembly has four rigid slotted arms on the hub which are used to bolt the disc to the hub. The arms are slotted to allow for the disc connection to slip radially along the arms caused by the thermal expansion of the disc. Vibration induced by track irregularities and thermal expansion and contraction of the disc causes slipping and fretting wear between the disc and hub connections which eventually produces wear in the connection. The wear can lead to impact loading of the connection members.
In view of the foregoing, it would be desirable to have a disc brake assembly which provides for the expanding and contracting discs and hubs, resists fretting and still withstands the high loads induced by braking.